Feeding pulverized fuel for combustion



Feb. 5, 1957 L v ANDREWS 2,730,186

FEEDING PULVERIZED FUEL FOR COMBUSTION FiledApril 14, 1950 L J/ANDREWJATTORNEY United States Patent FEEDING PULVERIZED FUEL FOR COMBUSTION L VAndrews, Worcester, Mass., assignor to Riley Stoker (ilorporation,Worcester, Mass., a corporation of Massac usetts Application April14,1950, Serial No. 155,959

1 Claim. (Cl. 110-106) This invention relates to the feeding ofpulverized fuel for combustion, and more particularly to an improvedapparatus for preparing pulverized fuel and transporting it on a currentof air directly to a furnace for combustion therein.

It is a common practice to grind coal or similar fuel to a fine powderin a suitable pulverizer, viz. a machine of the rotary beater type, suchapparatus usually including a fan arranged to produce a current ofso-called primary" air which carries the fine coal in suspension to afurnace burner. The rate of combustion is controlled by regulating thesupply of coarse coal to the pulverizer. An increase in the rate of coalfeed tends to reduce the rate of primary air flow through thepulverizer, and at high rates of coal feed the air flow may beinsufficient to remove fine coal from the pulverizer fast enough toprevent congestion in the pulverizer and overloading thereof. A furtherdifficulty is encountered in installations having two burners both ofwhich are connected to a single pulverizer to receive fuel and primaryair therefrom. If such an installation is adjusted to operate properlywith both burners in service, and an attempt is made to operate withonly one of the burners, it often is very diflicult to maintain ignitionof the fuel at the single burner.

It is accordingly one object of the invention to provide an improvedapparatus to prevent congestion and overloading in a pulverizer whichsupplies fine fuel to a furnace.

It is a further object of the invention to provide a simple anddependable apparatus to ensure proper ignition of fuel in aninstallation having two burners either or both of which may receive fuelfrom a single pulverizer.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

In accordance with the invention, the conduit through which the streamof pulverized fuel and primary air leaves the pulverizer is fitted withan adjustable valve, and the valve adjustment is varied as required tomaintain a predetermined pressure in the conduit beyond the valve. Thevalue of Lhis pressure is increased and decreased as the rate of fuelfeed to the pulverizer is increased and decreased, so that when morefine fuel is being produced there will be an increased flow of primaryair through the pulverizer to prevent congestion therein. Furthermore,this will ensure the correct flow of primary air to each burner whetherone or two burners are in service.

Referring to the drawings illustrating one embodiment of the invention,and in which like reference numerals indicate like parts,

The single figure is an elevation of a steam generating furnace firedwith pulverized coal and provided with certain automatic controlapparatus.

The embodiment illustrated comprises a steam generating furnace havingtwo burners 1112 through which pulverized coal and air are delivered tothe furnace for combustion therein to generate steam in a well-knownmanner, the steam being conducted by a steam outlet pipe 14 to a placeof use. The coal is ground to a fine powder in a suitable pulverizer 15having its delivery pipe 16 2,780,186 Patented Feb. 5, 1957 connected tothe burners 11-12 by two branch pipes 18-19 respectively. The pipes18-19 are provided with suitable valves 2021 respectively, so thateither burner may be taken out of service if desired. The pulverizer isprovided with a suitable feeding mechanism 23 which is supplied withcoarse coal from an overhead bunker 24 through a downspout 25. Thefeeding mechanism 23 is driven by a variable-speed electric motor 27which is supplied with electric current from a source 28 by means ofwires 29. A rheostat 31 is connected into the electrical circuit tocontrol the motor speed, the rheostat having a pivotally supportedoperating arm 32.

The pulverizer 15 is preferably of the rotary beater type adapted toreduce the coal to a fine powder and to deliver the powder, entrained ina current of primary air, through the pipe 16. One suitable pulverizerconstruction is disclosed in the prior United States patent to Craig,No. 1,714,080, granted May 21, 1929. By suitably controlling the flow ofthe primary air, highly beneficial results are obtained. For thispurpose a valve 34 is mounted in the pulverizer discharge pipe 16 andprovided with an operating arm 35, this arm being actuated by automaticregulating apparatus responsive both to the pressure within the pipe 16beyond the valve 34 and to the rate at which coal is supplied to thepulverizer.

The particular apparatus illustrated comprises a regulator 37 of thetype disclosed in the prior United States patent to Temple No.1,992,048, granted February 19, 1935. This regulator comprises a pilotvalve mechanism 38 supplied with fluid under pressure from a suitablesource through a pipe 39, the valve mechanism being connected by tubes40 to a hydraulic motor 42 which is connected by a link 43 to the arm 35of the valve 34. The pilot valve mechanism is actuated by a lever 44which in turn is controlled by a flexible diaphragm 45, the diaphragmbeing loaded by means of a coiled tension spring 47. The upper end ofthe spring is supported by a nut 48 mounted on a vertical screw 49 whichcan be raised and lowered by means of a lever 50. The pressure in thepulverizer discharge pipe 16, beyond the valve 34, is transmitted to theupper side of the diaphragm 45 by means of a pipe 52. In order toprevent this pipe from becoming blocked with coal dust, a fine screen orfilter 53 of any suitable construction is mounted in the pipe 52, nearits junction with the pipe 16. To facilitate cleaning of this screen, avalve 54 is provided in the pipe 52 near the screen, and a pipe 56having a valve 57 therein is connected to the pipe 52 intermediate thevalve 54 and the screen. This pipe 56 may lead from a suitable source offluid under pressure, such as compressed air. With the valve 54 closed,the valve 57 may be opened to blow air through the screen 53 into thepipe 16, thereby clearing accumulated coal dust from the screen.

The regulator lever 50 and the rheostat arm 32 are both controlled by aregulator 59 which is responsive to the demand for heat from the furnace10, as indicated for example by changes in the pressure of steam in thepipe 14. This regulator 59 is of the type disclosed in the United Statespatent to Temple No. 2,049,549, granted August 4, 1936, and it comprisesa diaphragm chamber 60 and a motor 61. The diaphragm chamber 60 isconnected by a pipe 63 to the steam pipe 14. The motor 61 is connectedby a link 64 to a cam lever 65 which engages one end of the lever 50 toadjust the same. A link 66 connects the upper end of the link 64 to therheostat arm 32.

The operation of the invention will now be apparent in the light of theabove disclosure. With both of the valves 20 and 21 open, the pulverizer15 will supply pulverized coal and primary air to both the burners 11and 12, the rate of coal supply being dependent upon the speed of thefeeder motor 27 which in turn will be under the control of the rheostat31. So long as the demand for steam is steady, the pressure in the steamoutlet pipe 14 will remain constant at a desired value, and thispressure will be transmitted through the pipe 63 to the diaphragmchamber 60 of the regulator 59, which will hold the cam lever 65 and therheostat arm 32 in fixed positions. With the valve 57 closed and thevalve 54 open, the pipe 52 will transmit the pressure in the pipe 16(beyond the valve 34) to the diaphragm 45 of the regulator 37.Consequently this regulator will act in known manner, through the motor42, to control the valve 34 as required to maintain a predeterminedpressure beyond the same. If now there is an increase in the demand forheat, as evidenced by a drop in the steam pressure in the pipe 14, theregulator 59 will respond by moving the links 64 and 66 downwardly,thereby readjusting the rheostat arm 32 to increase the speed of thefeeder motor 27 and also readjusting the cam lever 65 to raise the screw49 and increase the tension of the diaphragm loading spring 47. Thusmore coarse coal will be supplied to the pulverizer 15 by the feeder 23,and more pulverized coal will be supplied to the burners 11-12 to takecare of the increased demand for steam. As the tension of the spring 47increases, the diaphragm 45 and the lever 44 will be moved slightlyupward, actuating the pilot valve mechanism 38, and admitting fiuid tothe motor 42 so that the latter will open the valve 34 slightly further.This will increase the rate of air flow through the pulverizer, andincrease the pressure in the pipe 16 as required to counterbalance theincreased spring tension and restore the regulator 37 to a balancedcondition. This increase in the air flow will avoid any possibility ofcongestion in the pulverizer, as might otherwise occur with theincreased feed of coarse coal. Consequently the pulverizer will operatesatisfactorily even at very high loads, without danger of blocking orplugging thereof by accumulations of coal within the machine.

If the load on the furnace becomes so low that the operator wishes tocarry the entire load on a single burner, say the burner 12, he willclose the valve 20 and thereby 7 will operate under these conditions toclose the valve 34 cause the entire stream of coal and primary air fromthe sufiiciently to prevent any appreciable increase in the pressurewithin the pipe 16 beyond this valve, so that the air flow through theburner 12 will remain substantially constant, and ignition will bemaintained without difficulty.

It will be apparent that the invention provides a simple and effectivesolution for certain problems which have heretofore caused considerabledifficulty in the burning of pulverized fuel.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

A control system for a furnace of a steam generating unit having aplurality of burners of pulverized fuel, a conduit feeding each of saidburners, a main conduit supplying the feed conduits, and a pulverizersupplied with coarse fuel by an adjustable feeding means, said controlsystem comprising: a hydraulic motor whose piston is connected to andresponsive to the output of the steam generating unit, the piston beingconnected to the said adjustable feeding means for control thereof, adiaphragmtype regulator connected to said piston in order that thenormal diaphragm position is determined thereby, means for obtaining thestatic pressure in the main conduit, said means being connected to saidregulator for impressing said pressure on one side of the diaphragm, avalve for controlling the flow through the main conduit, a secondhydraulic motor connected to said valve for actuation thereof, a pilotvalve connected for controlling the hydraulic pressure in said secondhydraulic motor, said pilot valve being controlled by connection to thediaphragm of said regulator.

References Cited in the file of this patent UNITED STATES PATENTS Re.20,156 Hardgrove Nov. 3, 1936 1,787,407 Peebles Dec. 30, 1930 1,951,763Mittendorf et a1. Mar. 20, 1934 1,992,048 Temple Feb. 19, 1935 2,000,270Andrews et al May 7, 1935 2,003,985 Wallene June 4, 1935 2,172,317Dickey Sept. 5, 1939 2,212,125 Peebles Aug. 20, 1940 2,404,937 AndersonJuly 30, 1946 2,409,002 Smith Oct. 8, 1946 2,530,117 Dickey Nov. 14,1950

